Effect of substituents on the thermochromism of stilbazolium merocyanines incorporated in epoxy resin

► The thermochromic effect of merocyanines are substituted by donor–acceptor qualities. ► The size of thermochromic effect of dyes can be influenced by attaching substituents of donor–acceptor nature. ► The thermosensitvity dyes was dependent on an equilibrium between quinonoid and benzenoid form. ► The polarization of molecules that facilitate the formation of H-type aggregates. The thermochromic effect (in the range 283–333K) on the spectroscopic properties of stilbazolium merocyanine derivatives are substituted by groups of different donor–acceptor qualities (–H, –C(CH3)3, –NO2 and –OCH3) located in the ortho position to the carbonyl group of the quinonoid ring was examined. The samples were embedded in a polymer matrix from the epoxy resin. Results show that the size of thermochromic effect of stilbazolium merocyanines can be influenced by attaching substituents of different donor–acceptor nature. The smallest value of this effect was recorded for dye substituted by large tert-butyl groups, and the largest for derivative with –NO2 group substituent. The thermosensitvity investigated dyes was dependent on: (1) an equilibrium between quinonoid form and benzenoid form (zwitterion), (2) the polarization of molecules that facilitate the formation of H-type aggregates.